X-ray images are commonly used to facilitate medical diagnosis and/or treatment. An X-ray image may be acquired by emitting radiation from an X-ray radiation source toward a patient and by receiving a radiation field of X-ray radiation which emerges from a side of the patient opposite the radiation source. The radiation intensity at a particular location of the received radiation field represents the attenuative properties of internal patient structures which lie along a divergent line between the radiation source and the particular location of the radiation field. The radiation intensities of the radiation field therefore represent a two-dimensional projection image of these structures.
The benefits of X-ray imaging should be balanced against the radiation dose received by a patient during imaging. This balance is particularly delicate in the case of computed tomography (CT) imaging, which reconstructs a three-dimensional CT image of the patient based on many X-ray projection images. The X-ray projection images are acquired from various projection angles, and each acquisition delivers a corresponding radiation dose to the patient.
The radiation dose delivered to a patient during CT imaging may be reduced by adjusting the radiation tube current based on the size and shape of the patient. For example, a larger patient may be imaged using a larger tube current than the tube current used to image a smaller patient. Other parameters imaging such as tube voltage may also be adjusted, based, for example, on whether the CT image includes injected contrast agent. Systems are desired to further reduce the radiation dose delivered to a patient while achieving suitable image quality.